 /*******************************************************************************
  * Copyright (c) 2000, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.text.edits;

 import org.eclipse.core.runtime.Assert;

 import org.eclipse.jface.text.BadLocationException;
 import org.eclipse.jface.text.DocumentEvent;
 import org.eclipse.jface.text.IDocument;
 import org.eclipse.jface.text.IDocumentListener;


 class UndoCollector implements IDocumentListener {

     protected UndoEdit undo;
     private int fOffset;
     private int fLength;
     
     /**
      * @since 3.1
      */
     private String fLastCurrentText;

     public UndoCollector(TextEdit root) {
         fOffset= root.getOffset();
         fLength= root.getLength();
     }

     public void connect(IDocument document) {
         document.addDocumentListener(this);
         undo= new UndoEdit();
     }

     public void disconnect(IDocument document) {
         if (undo != null) {
             document.removeDocumentListener(this);
             undo.defineRegion(fOffset, fLength);
         }
     }

     public void documentChanged(DocumentEvent event) {
         fLength+= getDelta(event);
     }

     private static int getDelta(DocumentEvent event) {
         String text= event.getText();
         return text == null ? -event.getLength() : (text.length() - event.getLength());
     }

     public void documentAboutToBeChanged(DocumentEvent event) {
         int offset= event.getOffset();
         int currentLength= event.getLength();
         String currentText= null;
         try {
             currentText= event.getDocument().get(offset, currentLength);
         } catch (BadLocationException cannotHappen) {
             Assert.isTrue(false, "Can't happen"); //$NON-NLS-1$
 }
         
         /*
          * see https://bugs.eclipse.org/bugs/show_bug.cgi?id=93634
          * If the same string is replaced on many documents (e.g. rename
          * package), the size of the undo can be reduced by using the same
          * String instance in all edits, instead of using the unique String
          * returned from IDocument.get(int, int).
          */
         if (fLastCurrentText != null && fLastCurrentText.equals(currentText))
             currentText= fLastCurrentText;
         else
             fLastCurrentText= currentText;

         String newText= event.getText();
         undo.add(new ReplaceEdit(offset, newText != null ? newText.length() : 0, currentText));
     }
 }

